Not a good idea though. As you cannot reproduce that way, and hired workers are expensive on turn 1.
Where is this rule found? All I can find for reproduction is 2 citizens in the same region, with no 3rd meeple and neither a rebel. As for a split tile being one region, the migration example on pg 11, shows red migrating in that situation as:
"sea convoy across a sea inlet on the SAME region".
edit: Though looking some more, I see that harvest is worded the same way, with no allowance for sea dividing a region. That has me leaning to the sea divides a hex into two regions, but still can't find a specific reference to it.